This invention relates to regulated deflection circuits.
In many horizontal deflection circuits, energy is coupled to the deflection circuit from a source of B+ operating voltage through an input choke or horizontal output or flyback transformer. Conventional regulators for these circuits have included saturable reactors, the inductance of which is controlled to achieve regulation, or have included various types of switching arrangements.
One type of prior art regulator for SCR deflection, for example, provides for forward current regulation of the input operating current. In these forward regulators, an SCR is coupled in series with the B+ supply and the input choke. A phase controlled oscillator responsive to an energy level within the deflection circuit gates the SCR into conduction during the commutating interval of each deflection cycle. The SCR is commutated off during the noncommutating interval as the voltage across the commutating switch causes the current through the input choke and the SCR to decrease below the SCR holding current level. Regulation is achieved by varying the turn-on time or conduction angle of the SCR, thereby controlling the amount of energy provided by the B+ supply to the deflection circuit. Such a regulator is less suited for transistorized deflection, since the regulator SCR must be selected to withstand relatively large retrace pulses developed across the SCR after the SCR is commutated off.
Furthermore, forward current regulators without excess energy return capability exhibit a relatively large percentage change in conduction angle with changes in loading caused by various load circuits. The choice of control circuitry for the regulator is limited then to those capable of providing large conduction angle changes for the regulator SCR. Also, relatively large percentage conduction angle changes in transistorized deflection circuits due to load variation will result in relatively large percentage changes in peak output transistor collector currents causing undesirable raster distortion if not adequately compensated.
Another type of prior art regulator for transistorized deflection, for example, includes a regulating transistor in series with a flyback inductance and the unregulated B+ supply. Control signals to the transistor base vary the turn-on time within each trace interval for regulating the transistor conduction angle. The signals also turn off the transistor prior to the end of trace. A catch diode coupled to ground and the flyback inductance conducts the flyback inductance current when the transistor is nonconductive, during the retrace period and the beginning and ending intervals of the trace period.
In such a regulator design, the controlled switching element; i.e., the regulating transistor, must turn-off each deflection cycle while still conducting substantial amounts of operating current, resulting in undesirable switching dissipation and the production of relatively larger amounts of radio frequency interference (RFI).
To prevent the development of a retrace pulse across the regulating transistor, a relatively large inductance is required, thus necessitating a relatively large and more expensive iron core input choke, if a separate input inductance is used. The relatively large inductance would also require a relatively large conduction angle for the regulating transistor at a given load power consumption. Such large conduction angles may not be practical if the above transistor regulator design were to be adapted for SCR deflection circuits.
A third type of prior art regulator for SCR deflection, for example, provides for return current regulation of the input operating current. Typically, a diode is coupled in series with the input choke and the B+ supply. The diode conducts forward current during the commutating interval. A controlled switching element; i.e., an SCR, conducts return current to the B+ supply. Regulation is achieved by varying the turn-on instant during the latter portion of the noncommutating interval, thereby controlling the amount of energy returned to the supply and the net amount of energy coupled to the deflection circuit. Such regulators, however, are relatively unsuited for use in transistorized deflection systems because of the resulting relatively large undesirable modulation of the retrace pulses. Furthermore, relatively large retrace pulse voltages will be undesirably developed across the switching element during a portion of the retrace interval.